1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly relates to a technique for forming interconnects in a multilevel interconnection in which insulating films are formed between interconnect layers.
2. Description of the Related Art
In recent years, miniaturization of semiconductor integrated circuits has been significantly advanced, and the degree of integration has been tremendously increasing. As the number of devices integrated on a single semiconductor integrated circuit has been increasing, delay time is expected to be reduced. However, in practice, although transistor delay time can be reduced, wiring resistance and parasitic capacitance are increased, making it difficult to reduce wiring delay time. In order to lower wiring resistance, instead of conventionally used aluminum, copper having a lower resistance is used as a wiring material. Also, in order to reduce parasitic capacitance, insulating films having low dielectric constants are used as insulating films. Due to difficulties in patterning copper by etching, copper interconnects are typically formed by a Damascene process, in which after formation of a trench pattern, trenches are filled with copper, and then the upper surface of the copper film is planarized by a chemical mechanical polishing process to form interconnects.
FIG. 1 is a cross-sectional view of a conventional semiconductor device. As shown in FIG. 1, in the conventional semiconductor device, a second insulating film 2 which is relatively high in moisture absorbency is formed on a first insulating film 1 formed on a silicon substrate. In the second insulating film 2, contacts 3, each composed of a barrier metal film 3a made of titanium/titanium nitride or tantalum nitride/tantalum and a metal film 3b made of copper or tungsten, are formed through the second insulating film 2. A third insulating film 4 made of a silicon carbon nitride film is formed on the second insulating film 2. A fourth insulating film 5 is formed on the third insulating film 4. In the third and fourth insulating films 4 and 5, metal interconnects 9, each composed of a barrier metal film 9a made of tantalum nitride/tantalum and a metal film 9b made of copper or the like, are formed.
FIGS. 2A through 2D are cross-sectional views illustrating process steps for fabricating the conventional semiconductor device. A method for fabricating the conventional semiconductor device will be described in detail below.
First, as shown in FIG. 2A, contacts 3, each composed of a barrier metal film 3a and a metal film 3b made of copper or tungsten, are formed. To be specific, a first insulating film 1 is formed on a silicon substrate. Then, a second insulating film 2 having relatively high moisture absorbency is formed on the first insulating film 1. Next, a contact hole pattern made of a photoresist is formed on the second insulating film 2 by a photolithography process, and contact holes are formed by a dry etching process using the contact hole pattern. Subsequently, a barrier metal film 3a made of tantalum nitride/tantalum or titanium/titanium nitride is deposited on the bottoms and sidewalls of the contact holes so as to reach the upper surface of the second insulating film 2. Then, a metal film 3b made of copper or tungsten is deposited on the barrier metal film 3a so as to fill the contact holes. Next, part of the barrier metal film 3a and part of the metal film 3b formed outside the contact holes are removed by a chemical mechanical polishing process. As a result, the contacts 3 composed of the barrier metal film 3a and the metal film 3b made of copper or tungsten are formed.
Subsequently, as shown in FIG. 2B, a wiring groove pattern 7 is formed above the silicon substrate. Specifically, a third insulating film 4 made of a silicon carbon nitride film is deposited on the second insulating film 2 and on the contacts 3. Thereafter, a fourth insulating film 5 made of a carbon-containing silicon oxide film is deposited on the third insulating film 4. Then, an antireflection film 6 is deposited on the fourth insulating film 5. Next, the wiring groove pattern 7 made of a photoresist is formed on the antireflection film 6 by a photolithography process.
Next, as shown in FIG. 2C, wiring grooves 8 are formed in the fourth insulating film 5. To be specific, parts of the antireflection film 6 and parts of the fourth insulating film 5 are removed by dry etching in accordance with the wiring groove pattern 7, thereby forming the wiring grooves 8. Subsequently, the wiring groove pattern 7 and the antireflection film 6 are removed by ashing.
Then, as shown in FIG. 2D, metal interconnects 9 connected with the contacts 3 are formed. To be specific, parts of the third insulating film 4 defining the bottoms of the wiring grooves 8 are removed by etching, thereby exposing the contacts 3. Subsequently, a barrier metal film 9a made of tantalum nitride/tantalum is deposited on the bottoms and sidewalls of the wiring grooves 8 and on the fourth insulating film 5. Next, a metal film 9b made of copper or the like is deposited on the barrier metal film 9a so as to fill the wiring grooves 8. Then, part of the barrier metal film 9a and part of the metal film 9b formed outside the wiring grooves 8 are removed by a chemical mechanical polishing process. As a result, the metal interconnects 9 including the barrier metal film 9a and the metal film 9b are formed.